[MS ABI] Mangle unnamed empty enums (PR37723)

[hans]

Summary

Clang would previously assert here.

[hans]

Please take a look.

I couldn't figure out a way to get a mangled name for this without using debug info. Do you have any ideas?

[majnemer]

lib/AST/MicrosoftMangle.cpp

888–891

Thinking about it some more, it'd be better if we handled this like the else case:

Name += "<unnamed-type-$S";
Name += llvm::utostr(Context.getAnonymousStructId(TD) + 1);

Reason being that something like:

struct S {
  enum {};
  enum {};
};

Would otherwise end up with two identical mangles.

This would also make us more consistent with other mangles, for example:

enum {} x;
struct {} y;

These are mangled as: <unnamed-type-x> and <unnamed-type-y>.

[hans]

Thanks!

lib/AST/MicrosoftMangle.cpp

888–891

Okay, yeah that makes sense.

I just checked

struct S {

enum {};
enum {};

};

with MSVC, and they seem to give them identical mangling.

I have to head out, but will update the patch tomorrow morning unless you're keen to do it :-)

[hans]

Falling back to the "Otherwise, number using $S" code for non-empty enums.

[majnemer]

LGTM

lib/AST/MicrosoftMangle.cpp

case DeclarationName::Identifier: {
       } else if (TypedefNameDecl *TND =
                      Context.getASTContext().getTypedefNameForUnnamedTagDecl(
                          TD)) {
         // Anonymous types without a name for linkage purposes have their
         // associate typedef mangled in if they have one.
         Name += "<unnamed-type-";
         Name += TND->getName();
       } else if (auto *ED = dyn_cast<EnumDecl>(TD)) {
         auto EnumeratorI = ED->enumerator_begin();
-        assert(EnumeratorI != ED->enumerator_end());
+        if (EnumeratorI == ED->enumerator_end()) {
+          Name += "<unnamed-tag";
+        } else {
           Name += "<unnamed-enum-";
           Name += EnumeratorI->getName();
+        }
       } else {
         // Otherwise, number the types using a $S prefix.
         Name += "<unnamed-type-$S";
         Name += llvm::utostr(Context.getAnonymousStructId(TD) + 1);
       }
       Name += ">";
       mangleSourceName(Name.str());
       break;

test/CodeGenCXX/mangle-ms-cxx11.cpp

 // RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -fms-compatibility-version=19.00 | FileCheck %s --check-prefix=CHECK --check-prefix=MSVC2015
 // RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -fms-compatibility-version=18.00 | FileCheck %s --check-prefix=CHECK --check-prefix=MSVC2013
+// RUN: %clang_cc1 -std=c++11 -fms-extensions -emit-llvm %s -o - -triple=i386-pc-win32 -gcodeview -debug-info-kind=limited | FileCheck %s --check-prefix=DBG
 
 namespace FTypeWithQuals {
 template <typename T>
 struct S {};
 
 using A = int () const;
 S<A> a;
 // CHECK-DAG: @"?a@FTypeWithQuals@@3U?$S@$$A8@@BAHXZ@1@A"

 
 int call_it = (A::default_args(), 1);
 }
 
 enum { enumerator };
 void f(decltype(enumerator)) {}
 // CHECK-DAG: define internal void @"?f@@YAXW4<unnamed-enum-enumerator>@@@Z"(
 void use_f() { f(enumerator); }
+
+namespace pr37723 {
+struct s { enum {}; };
+// DBG-DAG: DW_TAG_enumeration_type{{.*}}identifier: ".?AW4<unnamed-tag>@s@pr37723@@"
+s x;
+}